Enhancing Co2 adsorption in sandstone formation using fly ash nanoparticles: A geo-sequestration approach

Abstract. A primary environmental concern making global warming worse is the continuous release of CO2 into the atmosphere. One feasible approach to this issue is the geo-sequestration of CO2 involving CO2 adsorption and sequestration in saline aquifer formations. This study explores the possibility of improving CO2 adsorption in sandstone formations by using fly ash nanoparticles, a by-product. Pre- and post-nano-treated Berea sandstone samples are tested for CO2 adsorption at pressures ranging from 0.1 to 10 MPa, temperature of 40°C, and salinity of 10 wt% NaCl. High-pressure-temperature volumetric CO2 adsorption equipment was used to quantify CO2 adsorption under reservoir conditions. The findings reveal that Xanthan Gum (XG) polymer concentration of 0.04 wt% stabilized and well-suspended the fly ash nanofluid, exhibiting a zeta potential below -32.2 mV. The findings revealed that the total CO2 adsorption was 45.07 mmol/g for the nano-treated sample and 41.56 mmol/g for the untreated sample. Additionally, the fly ash nano-treated sample demonstrated superior CO2 adsorption across all pressure points. Specifically, when CO2 reached a supercritical state over 7.38 MPa, the nano-treated sample showed a maximum CO2 adsorption of 39.17 mmol/g, while untreated samples reached 36.40 mmol/g. Adsorption isotherm analysis revealed that the Toth model provided the best fit for the experimental data, with an R2 value of 0.9708, indicating heterogeneous and multilayer adsorption behavior. The isotherm analysis suggests that multilayer adsorption, driven by van der Waals forces, was predominant due to the energy favorability of forming multiple adsorption layers rather than a monolayer. The study outcome suggests the feasibility of fly ash nanoparticles as a promising nanofluid to improve CO2 adsorption in CO2 geo-sequestration projects.